1. Field of the Invention
This invention relates to valves for automatically controlling the discharge of a slurry from the bottom of a solids-liquid separator, and more particularly to a pressure-responsive valve mechanism useful in reducing the fluid content of a slurry which is discharged from the bottom of a solids-liquid separator.
2. Description of the Prior Art
In many solids-processing operations, it is necessary to separate a solid material from a liquid, either to remove a solid contaminant from the liquid or to recover a solid product. In either case, a preliminary separation is often made by allowing the solids material to settle in a solids-liquid separator, and discharging a solid-liquid slurry of reduced fluid content from the bottom of the separator. It is the desire of the operator to discharge the solids from the separator accompanied by as little of the liquid as possible. For example, in the hot water-diluent processing of tar sand, the mined tar sand is placed in a pulper with hot water, surfactants, and a high API-gravity hydrocarbon diluent. The pulper, by stirring and agitation, converts the gross mixture into a slurry wherein the tar and other hydrocarbons are removed from the surface of the sand. This slurry is then conducted to a solids-liquid separator for separation of the sand and other dense particulate matter which settle to the bottom, and an oil-water emulsion is withdrawn from the top of the separator and conducted to a thickener for further processing. It obviously is desirable to discharge the solids with as little of the valuable oil-water emulsion as possible. Ideally, the solids would be fully compacted and would contain only one pore volume of fluid, which in the case of a sand-water slurry would be about 40 volume percent water, i.e., about 20 weight percent water. However, this degree of separation is not readily attainable by this method and a more realistic goal in the case of a sand-water slurry would be the discharge of a slurry containing no more than about 50 volume percent water.
Past attempts to reduce the fluid content of a slurry discharged from the bottom of a solids-liquid separator have employed such complex devices as a motor-driven star valve whose rotation varied with the attenuation of a radiation beam passing through the bottom of the separator. The attenuation of the beam was measured by a Geiger counter, whereby the greater the density of the slurry, the greater the attenuation of the radiation beam. This particular system resulted in abrupt on-off flow, thus not providing a smooth, continuous flow of a reduced fluid-content slurry. This system, as well as others, is also complex, difficult to adjust, and requires an external source of power.
Thus, there is a need for a simple, yet easily adjustable valve capable of discharging a reduced fluid-content slurry from the bottom of a solids-liquid separator, and particularly for one which does not provide abrupt on-off flow or require an external source of power.
Accordingly, a principal object of this invention is to provide a simple, efficient, and easily adjustable device for discharging a reduced fluid-content slurry.
Another object of the invention is to provide a device that functions automatically to reduce the fluid content of a slurry discharged from the bottom of a solids-liquid separator.
Still another object of this invention is to provide a device having a discharge capacity that varies inversely with the fluid content of the slurry, thereby avoiding abrupt on-off flow.
Yet another object of this invention is to provide a pressure-responsive device that functions automatically to reduce the fluid content of a slurry and which does not require an external source of power.
Further objects and advantages of this invention will become apparent to those skilled in the art from the following description.